1. Field of the Invention
The present invention relates to a self-locking and reversible mechanism for deploying the diverging portion of a rocket engine nozzle, the mechanism comprising three identical actuation assemblies mounted on a main frame fixed on a non-deployable portion of the nozzle.
It is common practice, in particular with the intermediate stages of launchers, to use rocket engine nozzles with deployable diverging portions that enable the outlet section of the nozzle to be adapted as a function of ambient pressure, which pressure falls off in going from low altitudes close to earth to high altitudes where the space vehicle leaves the earth's atmosphere, such that optimum thrust is conserved in spite of changing altitude.
The deployable portion of the nozzle must therefore be capable of being deployed automatically and reliably with minimum energy expenditure electrical, hydraulic, or pneumatic control means.
2. Prior Art
Different types of mechanism have already been proposed for deploying the deployable diverging portions of rocket engine nozzles, and in particular deployment mechanisms that are based on cable systems, ball screw systems, extensible beam systems, membrane systems, or spring systems.
Such known mechanisms are generally non-reversible, in other words once they provide a locking function, as with an extension beam system, for example, such locking in the deployed position is irreversible. These types of deployment mechanisms are therefore not adapted to vehicles such as space aircraft for which it is necessary both to deploy and to retract the diverging portion. In addition, some deployment mechanisms are fitted with electrically controled auxiliary locking devices that complicate implementation of the assembly and increase its mass.
Overall, the deployment mechanisms that have already been proposed are complex to implement, and are bulky or give rise to an increase in mass that constitutes a severe penalty for a space vehicle.
There is also known from document FR-A-2 568 316 a deployable diverging portion system having a single moving part that moves in translation parallel to the axis of the nozzle. Actuators displace the part along fixed columns disposed parallel to the axis of the nozzle.
Mechanisms have also been proposed for deploying a diverging portion that comprise actuator-and-linkage assemblies. Nevertheless, known mechanisms of this type are also bulky, not simultaneously lockable and reversible, and are not always adapted to rigid type deployable diverging portions.
Document U.S. Pat. No. 4,489,889 discloses a non-reversible deployment mechanism for the diverging portion of a rocket-engine nozzle, which mechanism makes use of an actuator associated with a linkage-and-cam system. Nevertheless, that relatively complex mechanism provides no self-locking, and in the deployed position the actuator must continue to be actuated, which tends to reduce reliability.
Document FR-A-2 622 931 describes an actuating mechanism for an extensible thrust nozzle of a rocket engine, comprising a linkage driven by actuators. The actuating mechanism described in that document includes separate control and guidance members which creates additional bulk, both in the folded position and in the extended position, without neither ensuring that the moving portion is automatically locked in its retracted and deployed positions, or providing reliable guidance on reaching its extreme retracted and deployed positions.